Monoscope cathode ray tube



A ril 15, 1969 K.- H. BRENNER, JR 3,439,215

. MONOSCOPE CATHODE RAY TUBE 'Filed May 1,1967

' /o K /9 COMPUTER DISPLAY /3 I MONOSCOPE A /7 2/ 7} PRINTER g SCAN v GENE/i4 70A i (WA/M67514 SEZECTOK INPUT VIDEO cum/r Z9 M N P a R INVENTOR.

r u v w Ku/rr H. .BKEN/Vifl k Z 5 & it BY ATTORNEY United States Patent 3,439,215 MONOSCOPE ATHODE RAY TUBE Kurt H. Brenner, Jr., Seneca Falls, N.Y., assignor to Sylvania Electric Products line, a corporation of Delaware Filed May 1, 1967, Ser. No. 634,994 Int. Cl. H01j 29/41 US. Cl. 315-12 3 Claims ABSTRACT OF THE DISCLOSURE A new monoscope tube wherein a character stencil is positioned between an electron gun and a signal plate. The video output signal is taken from the signal plate rather than the character stencil so that neither the signal plate nor the character stencil are susceptible to degradation from the electron beam in normal use. Since it is not necessary to use stencil material having controlled secondary electron emission properties, the fabrication of the character stencil is greatly simplified resulting in a more economical monoscope tube.

Background of the invention This invention relates generally to cathode ray tubes and more particularly to improved monoscope cathode ray tubes.

The monoscope is a well-known cathode ray tube used, for example, to generate electrical signals representing alpha or numeric characters for display purposes or used to generate electrical signals representing broadcasting test patterns. In general a monoscope contains a target electrode which is scanned by an electron beam. The target has selected portions which produce different signal levels as the target is scanned by the electron beam. In the prior art the target electrodes have generally been one of two types, the first being a stencil target with the desired character pattern represented by voids in the stencil. The target is scanned by the electron beam which upon striking the stencil surface generates secondary electrons. A collector band having a positive potential with respect to the target is disposed adjacent the target and collects the secondary electrons. The signal taken from the target varies in accordance with the number of secondary electrons emitted from the target format. The electron beam when passing through the voids in the stencil pattern does not generate secondary electrons and therefore establishes a zero reference level for the video signal. However, the monoscope using the target stencil has a serious disadvantage in that the stencil surface must be free of defects and have a uniform rate of secondary electron emission in order to maintain a satisfactory signal to noise ratio and a consistent level of video output. This generally requires careful processing, including microscopic inspection of the target stencil thereby adversely affecting the cost of the monoscope.

The second commonly used monoscope construction utilizes a target upon which a character matrix of high carbon content has been deposited. A collector band, positive with respect to the target, attracts secondary electrons released from the target background as it is scanned by an electron beam. However, as the electron beam strikes the carbon characters, relatively few secondary electrons are released so that the target is more negative when the beam scans the carbon matrix portion of the target. To provide adequate signal levels and a satisfactory signal to noise ratio, extreme care and cleanliness is required in processing the target plate. It is also necessary to inspect the final assembly under a microscope for surface defects or irregularities, which, if present, will cause rejection of the assembly. As a result, this type of monoscope tube assembly does not lend itself to production line methods.

In prior art monoscope tubes which rely on secondary emission for signal generation, it has been found that the secondary emission rate of the target material varies with age and use, such variation being most noticeable for those sections of the target which are more frequently scanned. Since the degradation of the secondary emission rate is not uniform over the surface of the target, the net result is a decreased video output signal at a given beam current, which will eventually render the tube unusable, that is, the effective tube life is shortened.

Accordingly, it is an object of this invention to provide an improved monoscope tube which overcomes the foregoing disadvantages and deficiencies of prior art devices.

It is a specific object of the present invention to provide an improved monoscope tube of simplified design and construction, which has improved video output signal characteristics.

Still another object of this invention is to provide an improved monoscope tube which does not require the careful, elaborate and costly construction methods of prior art tubes and therefore results in a more economical tube.

A further object of this invention is to provide an improved monoscope tube having a longer effective operating life.

Summary of the invention According to one aspect of the invention, a monoscope tube is constructed having the character stencil placed between the electron gun and a signal plate in a manner such that only those electrons passing through the voids in the stencil reach the signal plate. The signal representing the scanned character is taken from the signal plate, rather than the character stencil, so that the stencil does not require special surface treatment, preparation and inspection.

Description of the drawings FIG. 1 is a block diagram of a system in which the monoscope tube of the present invention finds utility;

FIG. 2 is a plan view of a character stencil as utilized by the invention; and

FIG. 3 is a schematic representation of a monoscope tube according to the present invention.

Description of the prefierred embodiments For a better understanding of the present invention, together with other and further objects, advantages, and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings.

Referring now to FIG. 1, there is shown a computer 10 having its signal outputs 11 connected to the input of a monoscope tube 13. A scan generator 12 also supplies input signals via lines 14 to the monoscope tube. The output of the monoscope tube is developed across a load resistor 15 and applied via an amplifier 17 to a display device 19 and a print out device 21. In operation, the scan generator 12 provides electrical scan signals to the tube 13, the scan signal comprising a scanning raster which effectively encompasse the dimensions of a single character. The inputs 11 from the computer 10 to the monoscope tube 13 are coordinate signals representing the location of the character on the stencil within the monoscope tube to be scanned. For example, referring to the illustration of the character stencil shown in FIG. 2, in order to accomplish the scan of the letter F, one input from the computer selects the first column of the stencil and a second input from the computer selects the fourth row of the stencil. The input from the scan generator is a scanning raster which is one character wide and one character high, i.e. encompasses the dimensions of the box 29 surrounding the letter F. Thus, by superimposing the input from the scan generator 12 on the inputs from the computer 10, the selected character and only that character is scanned by the electron beam. The video output is then developed across the load resistor 15 and applied via the amplifier 17 to the display 19 and the printer 21 for further signal processing.

Referring next to FIG. 3, a monoscope tube according to the present invention includes an electron gun 31 having its cathode connected to a source of energizing potential as represented by the terminal 33. A pair of vertical deflection plates 35 receive signal inputs which operate to control the vertical scan of the electron beam from the electron gun 31. In similar fashion, the horizontal scan of the electron beam is controlled by signals applied to a pair of horizontal deflection plates (not shown). An anode ring 37 is positioned between the electron gun 31 and a character stencil 39, the anode 37 being connected directly to a source of reference potential as represented by the terminal 40. A signal plate 41 is positioned behind the character stencil 39, the signal plate being connected via a resistor 15 to ground, and also connected directly to the input of an amplifier 17 which couples the signal to an output terminal 43 for further signal processing. The character stencil 39 is connected to a suitable source of energizing potential as represented by the terminal 45.

The operation of the monoscope tube of FIG. 3 depends upon the type of signal plate 41 used. According to one preferred embodiment, the surface of the signal plate facing the character stencil 39 is coated with a conductor having minimal secondary emission properties, such as carbon. With this embodiment the source of potential 33 applied to the cathode of the electron gun is negative, i.e. on the order of 1500 to -1800 volts. The anode band 37 is maintained near ground potential and the source of potential 45 applied to the character stencil 39 is slightly negative; for example, volts. The signal inputs applied to the deflection plates cause the electron beam to scan a selected portion of the character stencil. When the electron beam strikes the solid portion of the character stencil, the electrons do not reach the signal plate 41. However, as the beam scans the voids in the character stencil the beam passes unimpeded to the signal plate 41 and thus develops a signal potential across the load resistor 15. Since the signal plate surface has low secondary emission properties, very little signal strength is lost due to secondary emission. Furthermore, since the character stencil 39 is maintained at a negative potential with respect to the signal plate 41, the few secondary electrons which may be emitted at the plate surface are repelled by the negative potential on the stencil back toward the signal plate, thus yielding a stronger signal at the output across the load resistor 15. Since this embodiment does not rely on secondary emission properties to develop the signal output, the tube is relatively unaffected as the tube ages. Further, since the character stencil is not used directly to develop the output signal, variations in the stencil surface are relativel unimportant as long as the character cut-outs are sufliciently sharp.

According to another embodiment of the invention, the signal plate 41 is made from conductive material having high secondary emission properties. Again the cathode of the electron gun 31 is maintained at a high negative voltage and the anode band 37 is kept near ground potential. However, the character stencil 39 is connected to a source of energizing potential 45 which is positive, i.e. +50 volts.

The electrons of the electron beam passing through the voids in the character stencil 39 upon striking the signal plate 41 generate the emission of a high number of sec ondary electrons. Since the character stencil is positive with respect to the signal plate, these secondary electrons are attracted to and collected by the character stencil,

thereby resulting in a positive potential on the signal plate which is developed across the output load resistor 15. It has been found that a signal plate surface having high, uniform secondary emission properties can be easily fabricated and this embodiment permits the generation of a given output signal level using a relatively low electron beam current. Since a lower beam current is utilized, the tube life is extended and further provides a higher resolution electron beam resulting in a cleaner video output signal.

It is, therefore, readily apparent that the present invention provides significant advantages over prior art devices. Because the character stencil 39 acts only to shape the characters, and not as a signal source, there are no stringent requirements placed on the fabrication of the stencil resulting in a more economic design. The signal plate may be easily fabricated since it is only necessary to provide a uniform surface of high or low secondary emission material depending on the embodiment used.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

I claim:

1. A character generating cathode ray tube comprising:

an elongated tube envelope;

an electron gun positioned near one end of said tube envelope and arranged to provide an electron beam along the axis of said envelope;

a signal plate positioned near the opposite end of said tube envelope arranged transversely in the path of said electron beam, said signal plate comprising a material having a high secondary electron emission rate;

an output terminal connected to said signal plate;

a character stencil having a multiplicity of voids therein, to thereby define a multiplicity of characters, said stencil positioned in said tube envelope between said electron gun and said signal plate and arranged transversely in the path of said electron beam;

a source of reference potential adapted to be connected to said character stencil, said source of reference potential having a polarity and a magnitude operative to maintain said character stencil positive with respect to said signal plate; and

deflection means operative in response to input signals to cause the electron beam to scan selected sectors of said character stencil.

2. The invention according to claim 1 additionally comprising an anode ring positioned within said tube envelope between said electron gun and said character stencil.

3. The invention according to claim 1 wherein said deflection means comprise first and second pairs of electrostatic deflection plates positioned within said tube envelope between said electron gun and said character stencil to control, respectively, the horizontal and vertical scanning of said electron beam.

References Cited UNITED STATES PATENTS 3,278,794 10/1966 Boscia et al 315-12 X 3,336,497 8/1967 Osborne 315-18 3,336,498 8/1967 Castanera 3l518 RODNEY D. BENNETT, Primary Examiner.

C. L. WHITHAM, Assistant Examiner.

U.S. c1. X.R. 315 21; 340-324 

